1. Field of the Invention
The present invention relates to novel vehicles for introducing one or more compounds of the phenoxarsine family of biocides into starting mixtures which can be utilized in manufacturing processes for plastic materials.
2. Description of Related Art
10,10′-oxybisphenoxarsine (hereinafter referred to as “OBPA”) is a biocidal agent known to be suitable for use in plastic materials such as, for example, flexible polyvinyl chloride (hereinafter referred to as “flexible PVC”). In the course of manufacturing the plastic material, OPBA is typically incorporated via a solution including OBPA as a solute and one or more solvents. The solvent may subsequently perform a beneficial role, such as that of plasticizer, in the manufacturing process. At a minimum, the solvent should not detrimentally affect the properties of the finished plastic material.
Using a more concentrated OBPA solution rather than a less concentrated OBPA solution tends to reduce shipping costs and storage costs. While the plastics manufacturing industry generally utilizes solutions including in the range of about 1 to about 3 wt % OBPA, solutions including 5 wt % OBPA or more are desirable.
Because the solubility of OBPA in those plasticizers currently favored for manufacturing flexible PVC is less than 1 wt %, it has long been industry practice to dissolve OBPA in a combination of solvents, known as co-solvents, so that a more concentrated solution of the OBPA can be supplied to the flexible PVC manufacturer. The use of appropriate co-solvents tends to ensure that the OBPA dissolves completely, and remains dissolved, in the OBPA solution.
Representative plasticizers for manufacturing plastics include diisodecyl phthalate, 2-di (2-ethylhexyl) phthalate, polypropylene glycol, butylbenzyl phthalate, and epoxidized soybean oil, among others. For manufacturing flexible PVC, dioctyl diphthalate, diisononyl phthalate, diisodecyl phthalate and butyl benzyl phthalate are commonly employed as plasticizers. While these traditional plasticizers are utilized as solvents or co-solvents for OBPA, none has proven entirely satisfactory.
A typical OBPA solution includes an alcohol as a first co-solvent and a plasticizer as a second co-solvent. More specifically, an OBPA supplier may provide a flexible PVC manufacturer with a solution of 1 to 5 wt % OBPA, 8 to 20 wt % of an alcohol and 75 to 90 wt % of a plasticizer. Such an OBPA solution is routinely exposed to extremes of heat and cold during transportation and storage. Despite these temperature extremes, the OBPA solution should not exhibit any evidence of precipitation, phase separation or clouding. To the contrary, the OBPA solution should remain in the form of a clear, homogenous liquid until such time as it may be added to the flexible PVC manufacturing process during a compounding operation, which may be a “plastisol blending operation” or a “dry blending operation,” among others.
The compounding operation traditionally incorporates performance additives into flexible PVC in order to increase its usefulness. The additives may be, for example, plasticizers to increase the flexibility of the finished product, heat stabilizers to prevent degradation and discoloration of the PVC at the elevated temperatures required for processing, lubricants to improve the flow of the molten PVC and to prevent its sticking to metal processing surfaces, fillers to increase the bulk and lower the cost of the final material, and pigments to produce the desired color, among others.
In the compounding operation, the OBPA solution and the performance additives are mixed with resins and stirred at a temperature in the range of about 93-107° C., which range is below the fusion temperature of the resins. In the case of dry blending, resin particles imbibe the liquid and the result is a powder barely distinguishable in appearance from the original resin. In the case of plastisol blending, the result is a liquid. In either dry blending or plastisol blending, the resulting powder or liquid may be subsequently stored or fed directly to fabricating equipment where relatively high temperatures produce a fused compound in the manufacturing process.
Over the years, a number of co-solvents have been proposed for dissolving OBPA. For example U.S. Pat. No. 3,288,674, issued to Yeager, describes the use of solvents which are phenols, such as nonylphenol. Other patents mention the use of aliphatic alcohols as well as certain phosphites and phosphonates, such as tris(dipropyleneglycyl)phosphate.
Several of these co-solvents have been commercially successful, but none is entirely satisfactory. For example, isodecyl alcohol, which is currently used as a commercial co-solvent, is associated with irritation to human beings during the high temperature processing of flexible PVC.
U.S. Pat. No. 5,488,065, issued to Roth, describes aromatic alcohols, such as benzyl alcohol, as co-solvents which are less irritating to humans. Reportedly, benzyl alcohol produces less odor and irritation, as compared to nonyl phenol and isodecyl alcohol. However, benzyl alcohol cannot be considered a final answer because it does not completely eliminate irritation to humans, and because it contains an undesirably high amount of volatile organic carbon (hereinafter referred to as “VOC”).
The use of VOC's in the United States of America is regulated by both federal and state governments. While the various governmental entities sometimes adopt different definitions, the U.S. Code of Federal Regulations defines VOC in 40 CFR Part 51.100(s) as “any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions” and is not specifically exempted or exempted by demonstrated performance under certain standardized test conditions. In order to facilitate compliance, the plastics manufacturing industry is likely to welcome alternative co-solvents which perform well and are not classified as VOC's.
Each of the above-described vehicles or solvents has one or more disadvantages or deficiencies which make them less than ideal as a vehicle for OBPA. Many contain undesirable VOC's. Some have troublesome odors, low dissolving capacity at room temperature, relatively high viscosity, unsatisfactory miscibility with the plasticizers usually used in the plastic materials industry, unsuitable toxicological properties and the like. Accordingly, a need exists for an improved solvent or co-solvent for introducing OBPA into a manufacturing process for plastic materials.